The lichen flora of the county of Gwynedd, north-west Wales, is described. The flora includes 851 species and 19 subspecies and varieties. The work comprises sections on: climate; geology; land use and vegetation; history of lichenology, 1680–1985; corticolous flora, with classification and description of the important woodland sites; inland saxicolous flora, dealing with acid, intermediate and basic rock, the effects of altitude and aspect, the flora of seepages, streams and lakes; heath and moorland flora; coastal flora classified into the recognized zones of the marine littoral, mesic, submesic and xeric supralittoral; aspects of conservation, pollution; and the lichen flora itself. The latter includes a brief description of the ecology and distribution of each species and all of the currently known 10-km2 records for the species in the county.

Notes are provided on the genus Vezdaea and its five species represented in the British Isles, including V. acicularis sp. nov. A key to the six European species is included.

Choreospora tibellii P. Const. & R. Sant. gen. & sp. nov., a sporodochial hyphomycete with non-septate, tetraradiate conidia is described from Australia. The fungus grows on a sterile foliicolous lichenized thallus (?Echinoplaca sp.) on leaves of Cordyline.

The lichen Diploschistes muscorum (Scop.)R.Sant. starts its thallus development as a parasite of the squamules of different Cladonia species, but fully developed Diploschistes thalli live independently. D. muscorum develops apothecia in the Cladonia squamules and is associated at that stage with the phycobiont of Cladonia, Trebouxia irregularis. Augmentation of the Cladonia phycobiont and growth of the D. muscorum hyphae result in a development of young Diploschistes thalli from the Cladonia squamules. As the Cladonia increasingly disintegrates, D. muscorum becomes independent. In fully developed thalli the Cladonia phycobiont can be exchanged for T. showmanii, an alga different in morphology and reproduction from T. irregularis. In one case, a fully developed D. muscorum thallus with both phycobionts was demonstrated. A fully established thallus can also be formed by the growth of small thallus swellings, which cover Cladonia squamules.

The localization of norstictic acid and copper in green, copper-rich specimens of Acarospora smaragdula and Lecidea lactea from cupriferous substrata was studied by optical microscopy, scanning electron microscopy, and electron probe microanalysis. Infrared absorption spectroscopy of lichen material and a synthetic Cu-norstictic acid complex, and the other studies, provide evidence that complexing of copper by norstictic acid occurs within the cortex of these lichens and leads to their unusual surface coloration. Preliminary observations suggest that copper may also form a complex with psoromic acid and colour lichen thalli green. There is a strong possibility that other metal-lichen acid complexes may occur.